The present invention relates to a method of preserving certain raw materials prior to the secondary treatment of such materials to form a stable and therefore more usable end product. More specifically, the invention relates to a method of treating organic material, such as raw animal hides and skins, wherein the material is exposed to a combination of dilute antiseptic, and electron beam irradiation, to temporarily preserve the material prior to further treatment which stabilizes the skins and hides for end product use.
There is a need to introduce a new method to cure and preserve green hides and skins that can alleviate the hide industry's pressing problems of environmental pollution, transport container damage and increasing material and labour costs. Current methods for curing and preserving hides and skins, collectively referred to hereinafter as hides, use different chemicals, principally salt (NaCl), that are becoming increasingly difficult to dispose of in safe, economic and environmentally acceptable ways.
Hides flayed from slaughtered animals are delivered in bulk to a processing facility on or off the abattoir premises. The sequence of steps in the processing of the hides may vary from facility to facility, but generally speaking, the hides are initially soak washed, and trimmed. Washing removes soil, cools and softens the hides, and, assuming the use of recirculated cool water, the resulting depressed temperatures slow bacterial growth. The hides are trimmed to remove remaining extremities including the ears, tail, metal rings and larger pieces of flesh. The hides are conveyed via the trimmer from the washer to a demanuring and fleshing machine which removes unwanted flesh from one side of the hide, and manure from the other. The hides are then weighed and graded according to animal type and prefleshing quality, and records of the grading are kept. The hides are then cured. Conventional curing in the industry today most often involves the brine curing of the hides using either of the raceway or vat cure methods of brine curing commonly in use. The hides are soaked in a concentrated salt solution for up to 20 hours during all or part of which time they may be agitated. The brine cured hides are removed from the vats or raceways, and are then folded, stacked and palletized for medium to long term storage prior to tanning. Additional salt is sometimes simply poured onto each hide prior to folding for additional preservation. The cured hides are purchased by tanners who convert them into the stable end product universally known as leather.
A significant problem of the hide and skin industry today revolves around the intensive use of salt and brine. Curing itself is relatively inexpensive, but the ensuing salt disposal problems are becoming so significant as to threaten the closure of the domestic industry. Salt is used for its osmotic characteristics on cells which force water out of the cells of bacterial and animal flesh, thereby inactivating the aqueous intracellular medium needed for the unwanted decay of the hides. Once rehydrated, hides cured in this manner are prone to rapid decay.
Disposal of the salt, usually common sodium chloride, is becoming increasingly difficult and expensive due to increasingly stringent pollution limits. Salt is a problem not only to the processor, who must dispose of up to 2 gallons of brine per hide (3,000 to 14,000 gallons per day), but also the tanner who may have to wash out similar amounts of salt.
Problems of uneven salt distribution to the hides exist, and burns, stains and pitting due to salt are not uncommon. Downstream tanning costs are increased due to the extended times required to rehydrate the hides and remove the salt, and the unevenness of the process may require expensive handling variations sometimes on an individual hide basis. A salt or brine cured hide will yield up to 3% less product than a green hide. Salt curing often requires a cationic detergent prewash of the hides to increase the susceptibility of the hides to brine permeability. The detergents themselves may be environmentally harmful and costly to dispose of. Brine curing often requires the addition of chlorinated phenols following the cure to extend preservation, and such phenols are deadly to aquatic plant and animal life.
Other alternatives to salt curing include the use of biocidal antiseptics, refrigeration and sulfite preservation. However, environmentally acceptable concentrations of biocides alone cannot preserve a hide on average for more than 5 days. Refrigeration is much too expensive to be practical even on a large scale basis, and sulfites are coming under increasing regulatory control.
Radiation treatment has been investigated as a means for short to medium term hide preservation. In an unpublished paper presented at the American Leather Chemists Association in June, 1984, D. G. Bailey and M. J. Haas reported on the results of their investigations into the use of electron beam radiation to sterilize and preserve fresh hides. Bailey found that through singular use of electron beam radiation, the dose levels required to attain sterility are close to, and sometimes exceed, the tolerance dose that will cause damage to the hide and subsequent hide products. Other researchers, including T. A. Du Plessis et al., have reported on the results of similar experimentation using gamma radiation (Radiat. Phys. Chem. Vol. 22, No. 3.5, pp 491-501, 1983).
Du Plessis's work investigated the use of gamma radiation in combination with an antiseptic pretreatment of the hides. For various reasons, not the least of which includes the relatively unattractive economics of cobalt as a radiation source for the treatment of laminar products such as animal hides, and the inability to effectively control dose rates from natural isotope sources, such research has not yet resulted in the proposal of an acceptable alternative to traditional brine curing.